Long-range and vertical transport, troposphere-stratosphere exchange

Most long-range transport (LRT) models use a Lagrangian approach in which air mass trajectory shows the pathway of an air parcel having vertical and horizontal dispersion. The climatology of the flow within the boundary layer in the western Mediterranean (WM) obtained by two trajectory models yielded similar results. An airflow pattern performed over the eastern Mediterranean (EM) revealed five major source regions with the highest frequency originating from the north-western sector. Other flow climatology studies over Greece and Turkey during summer revealed consistent results indicating that these predominant flow directions point to central and north-eastern Europe as potential source regions. The LRT conditions in the upper troposphere differ between the EM and WM. In the western part, whatever the season is considered, air masses are basically coming from the west. However, in the EM, apart from the westerlies' influence, air masses are also originating from Asia, as evidenced in a study as part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx), using satellite measurements and model simulations. From a vertical transport perspective, evidence has been shown on stratosphere-troposphere exchange (STE), pointing to some dynamic factors that favor such a cross-tropopause transport over the eastern Mediterranean in summer.